Enhanced design of the quasi-zero stiffness vibration isolator with three pairs of oblique springs: Theory and experiment

Quasi-zero stiffness vibration isolators have been extensively studied due to superior passive vibration isolation performance. As the quasi-zero stiffness region of the isolators is generally small, the research on their responses to the excitation with high amplitude is currently quite limited. This paper presents an improved design of the quasi-zero stiffness isolator with three pairs of oblique springs to increase the amplitude of the excitation. Theoretical formulations are derived for stiffness and force, and then the influences of three independent parameters on the quasi-zero stiffness region are studied to obtain optimal design parameters. A prototype is fabricated and tested for displacement excitations with amplitudes of 5 mm, 10 mm, and 15 mm in a frequency range of 1.5-10 Hz. The absolute displacement transmissibility of the enhanced quasi-zero stiffness isolator is theoretically and experimentally compared with that of the corresponding linear isolator and that of the previous isolators with three pairs of oblique springs using the same parameter conditions of the loaded mass, the horizontal length of oblique springs, and the vertical spring. The experimental results show that the enhanced design of the quasi-zero stiffness isolator with three pairs of oblique springs can achieve lower displacement transmissibility and deal with the displacement excitation with higher amplitude.